The present invention relates to a printing device for exposing a photosensitive sheet of paper with a combination of a semiconductor laser and a semiconductor-laser-pumped solid-state laser, and a color printer which incorporates the printing device
There have been proposed various color printers. One color printer is of the intermediate image production system wherein intermediate images of R (red), G (green), and B (blue) colors are produced, and a photosensitive sheet of paper is exposed three times to the lights bearing these three-color images. Another color printer system includes a dichroic mirror for combining laser beams emitted from respective R, G, B laser beam sources into a single laser beam which is deflected by a deflecting optical system to scan a photosensitive sheet of paper wound on a drum. According to the latter system, the laser beam sources used are gas lasers of a red semiconductor laser, green and blue lasers which are composed of a combination of a wavelength converter and a semiconductor-laser-pumped solid-state laser.
The intermediate image production system has its resolution limited by the accuracy with which the three-color images are registered and also by the device which produces the intermediate images. The laser beam sources used in the system in which the photosensitive sheet of paper is exposed to the laser beams in three colors, should preferably be a semiconductor laser and a semiconductor-laser-pumped solid-state laser from the standpoints of reliability, service life, and cost. Since the modulation speed of the semiconductor-laser-pumped solid-state laser is limited by the fluorescent lifetime of the solid-state laser, however, the modulation speed required by a printer cannot be obtained simply by directly modulating the semiconductor laser.
Therefore, the printer requires a modulation device, but the modulation device is complex in structure and expensive. The modulation device also makes it difficult to render the printer compact.